Zongren Wang

Failure Analysis of Aviation Torsional Springs

Cracks and fractures occur during the assembly process to a type of torsional springs used in the aviation mechanism. Besides visual examination, other experimental techniques used for the investigation are: 1) fracture characteristics, damage morphology and fractography by scanning electron microscopy (SEM), 2) spectrum analysis of covering, 3) metallographic observation of cracks and 4) hydrogen content testing. The results are obtained through the analysis of manufacture process and experimental data. Since no changes of microstructure are found, failures are irrelevant to the material. The cracks and fractures initiate on the inner surface, cracks initiate before the cadmium plating and after the winding. No obvious stress corrosion cracks are found near the crack source region. The opening direction of cracks is consistent with the residual tensile stress of the spring inner surface, and the springs are easy to contact hydrogen media between the spring winding and the cadmium plating. The cracks are caused by hydrogen-induced delayed cracking under the action of the residual tensile stress and hydrogen.

Failure Analysis of Cracks in the Upper Shaft of Torque Arm

In the periodic inspection of a plane having flown for 300 h, cracks were found in the upper shaft of the torque arm of the landing gear. In addition to visual examination, other experimental investigation techniques were 1) crack morphology and fracture characteristics by scanning electron microscopy, 2) metallographic observation of cracks, 3) chemical constituents and hydrogen-content testing, 4) hardness testing, 5) impact and bending simulation test, and 6) comparison of wear condition for the crack-free upper shafts with other batches. The results were obtained through the analysis of processing and experimental data. Because of higher surface frictional shear stress and tensile stress, the cracks propagated in the form of stress corrosion after the initiation, which was unrelated to the coating, matrix material, and hydrogen content.

Investigation on Thermal Contact Conductance Based on Data Analysis Method of Reliability

Abstract The method of reliability is proposed for the investigation of thermal contact conductance (TCC) in this study. A new definition is introduced, namely reliability thermal contact conductance (RTCC), which is defined as the TCC value that meets the reliability design requirement of the structural materials under consideration. An experimental apparatus with the compensation heater to test the TCC is introduced here. A practical engineering example is utilized to demonstrate the applicability of the proposed approach. By using a statistical regression model along with experimental data obtained from the interfaces of the structural materials GH4169 and K417 used in aero-engine, the estimate values and the confidence level of TCC and RTCC values are studied and compared. The results show that the testing values of TCC increase with interface pressure and the proposed RTCC model matches the test results better at high interface pressure.

Crack Analysis of the Fourth-Stage Compressor Blades

crack morphology and fracture characteristics by video microscope and scanning electron microscopy, metallographic observation of the cracks, and energy spectrum analysis. The results were obtained through the analysis of the processing andexperimental data. The cracks are all fatigue cracks with multisource and line source, the main reason of which is concerned with higher contact stress during the assembly process after the first overhauling. The fretting wear between the tenon and the tenon-groove mating surface promotes crack initiation, which was unrelated to the material and processing.